JLH Headphone Amp - Page 29 - diyAudio
Go Back   Home > Forums > Amplifiers > Headphone Systems

Headphone Systems Everything to do with Headphones

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 6th November 2012, 06:43 PM   #281
diyAudio Member
 
Join Date: Jun 2011
Location: Canarias
I´ve got Ebay´s old version (green board) and the sound is not bad, no noise or HUM, but the offset is a really nightmareĦĦĦ

I can´t keep this parameter controlled around 50mV.
  Reply With Quote
Old 6th November 2012, 07:44 PM   #282
oz7aff is offline oz7aff  Denmark
diyAudio Member
 
oz7aff's Avatar
 
Join Date: May 2012
Location: Denmark
How about building at servo for it ?
__________________
Regards Max
  Reply With Quote
Old 6th November 2012, 08:40 PM   #283
bkercso is offline bkercso  Hungary
diyAudio Member
 
Join Date: Nov 2009
Location: Hungary
Try to use 4x1N4148 instead of 2.7V Zener.
If you trim the DC offset to 0V after warm up you get about 100mV when amp is cold (and vice versa). Try to trim around 50mV after warm up and when cold get -50mV (or vice versa? ).

Last edited by bkercso; 6th November 2012 at 09:00 PM.
  Reply With Quote
Old 7th November 2012, 06:13 PM   #284
diyAudio Member
 
Join Date: Jun 2011
Location: Canarias
Thanks guys

I've been working for a very little time in the amp because I´ve got another headphones amp (B22...)

I´ve made some changes on the original JHL,like this:

A) Trimpot 10k (20 turn off)
B) Nichicon Non polar (1000uF/25volt) on the out put.

I haven´t got any DC Servo.

As much the temperature grows, the offset change too.
  Reply With Quote
Old 7th November 2012, 06:25 PM   #285
diyAudio Member
 
Join Date: Jun 2011
Location: Canarias
Quote:
Originally Posted by bkercso View Post
Try to use 4x1N4148 instead of 2.7V Zener.
If you trim the DC offset to 0V after warm up you get about 100mV when amp is cold (and vice versa). Try to trim around 50mV after warm up and when cold get -50mV (or vice versa? ).
Well, the board have got 6x1N4148 but if you take a look, two others missing

Click the image to open in full size.
  Reply With Quote
Old 7th November 2012, 08:04 PM   #286
oz7aff is offline oz7aff  Denmark
diyAudio Member
 
oz7aff's Avatar
 
Join Date: May 2012
Location: Denmark
Quote:
Originally Posted by blackdod View Post
B) Nichicon Non polar (1000uF/25volt) on the out put.
Because you got these I think that you don't have to care about the offset as long it stayes below something like 100 mV
__________________
Regards Max
  Reply With Quote
Old 8th November 2012, 06:27 PM   #287
diyAudio Member
 
Join Date: Jun 2011
Location: Canarias
Thanks Max

Well, the offset is around 140 mVolt when the my amp is warm (with the Non Polar Cap) and I don´t like this. IMHO, 140 mVolt is very dangerous for a headphone. I supposed that with this Cap, the offset would have be around 0 mVolt.

I´m thinking change the input cap for a Wima 1uF or add other Non Polar Cap on the output (on series) ż?
  Reply With Quote
Old 8th November 2012, 07:11 PM   #288
oz7aff is offline oz7aff  Denmark
diyAudio Member
 
oz7aff's Avatar
 
Join Date: May 2012
Location: Denmark
Do you have schematic of the Amp ?

My headphones have a resistance of 160 Ohm's, so with 140 mV offset the current will be under 1 mA and that will not harm the phones in any way.

Ps: is the headphones connected to the amp through a capacitor ?
__________________
Regards Max
  Reply With Quote
Old 8th November 2012, 07:33 PM   #289
diyAudio Member
 
Join Date: Jun 2011
Location: Canarias
Quote:
Originally Posted by oz7aff View Post
Ps: is the headphones connected to the amp through a capacitor ?
Yes; amp out put--cap--headphones

Quote:
Originally Posted by oz7aff View Post
Do you have schematic of the Amp ?

My headphones have a resistance of 160 Ohm's, so with 140 mV offset the current will be under 1 mA and that will not harm the phones in any way.
Yes I have got the schematic and a fantastic article by Papa Nelson

But reality, I don´t want to spend much time on this amplifier.

I have some headphones, from 32 Ohm to 600 Ohm.

Regards
  Reply With Quote
Old 8th November 2012, 10:23 PM   #290
oz7aff is offline oz7aff  Denmark
diyAudio Member
 
oz7aff's Avatar
 
Join Date: May 2012
Location: Denmark
Quote:
Originally Posted by blackdod View Post
Yes; amp out put--cap--headphones
Then there should be no offset at all, the cap must be bad, must have a very large leakage.

Ps: the hole meaning of capacitors is that you can't put DC trough them, only AC.
__________________
Regards Max
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
JLH headphone amplifier steveh49 Headphone Systems 8 14th May 2014 03:31 PM
JLH Headphone amp aethelbert Headphone Systems 4 13th July 2009 11:14 PM
JLH headphone amp with FET's and servo nelsonvandal Headphone Systems 17 30th August 2008 09:26 PM
PCB for JLH amp FaTTy Solid State 0 27th March 2007 04:40 PM


New To Site? Need Help?

All times are GMT. The time now is 06:51 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright İ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2